Field of the Invention
The present teachings are directed to methods of producing a carbon coated particle with both high magnetic moment and high adsorption capacity.
Discussion of the Related Art
There are a number of reports on the use of carbon-based magnetic adsorbents. Various carbon allotropes can be attached to magnetic particles to provide high capacity, and high surface areas adsorbents, and combined with magnetic particles allows for magnetic guided delivery of drugs or removal of various pollutions, such as oil, heavy metals, radionuclides, etc., upon adsorption. However, one of the common drawbacks of these materials is the relatively weak saturation magnetism, which is vital for removal of adsorbed pollutions or for controlled drug delivery in an organism. Additionally, many of the known adsorbents are very small, typically less than 40 μm, which can in some instances make removal of the particles difficult.
In US 2010/0059449 A1, Grass et al. describe nanoparticles having a core shell type structure with a metallic core but with “soft” magnetic properties.
Tsang et al. in US 2005/0116195 A1 describe forming microparticles with a ferromagnetic core encapsulated in a graphitic shell containing hetero atoms. The hetero atoms can be catalytically active metals on the external surface for liquid phase reactions. Their process is described as having a pyrolysis temperature that must be sufficient to form the core and the graphitic coating at the same time.
Miller et al. teaches a method of mixing an iron magnetic precursor with a carbon precursor which is then pyrolyzed at high temperatures to form activated carbon particles with the magnetic material dispersed throughout the structure. See U.S. Pat. No. 8,097,185 B2.
The magnetic saturation of bulk iron is about 220 emu/g which can provide a strong interaction between an iron particle and an external magnetic field. However, for adsorbent properties, the surface area of bulk iron is quite low, usually less than 10 m2/g. Furthermore, iron tends to oxidize easily to the ferric and ferrous states which have magnetic saturation values of about one-third the value of bulk iron.
There is a need for a method of preparing carbon allotrope-based magnetic adsorbents with high levels of both magnetic moments and adsorption.